The measurment to tooth mobility has been recognized clinicaly as an important method to evaluate periodontal legament and other periodontal states. An objective attracted a lot of attention. In order to establish an objective evaluation method for periodontiume, including tooth mobility, this project study groupe has been developed an instrument "Damped Oscillation System" an studied dynamic parameter change (damped natural frequency, elastic constant, viscous constant and the ratio of elastic constant to viscous constant) by diff-erent conditon of Damped Oscillation including the position of sennsor, the size, shape and number of root model. And also, a comparative study with two commercial instrument, "perio-test" and "tooth mobility checker" were compleated, in advance to clinical use.Results are followed :1)In the case of moving the position of the detecing sensor horizontaly by hammer tappings from both horizontal and vertical directions, all values of the dynamic parameter decre
… Moreased as the distance between the detecting sensor and the tooth model increased.2)In the case of moving the position of the detecting sensor verticaly by horizontal tapping, the dynamic parameter increased as a distanse between the detecting sensor and the top of the tooth model increased, except the ratio of elastic constant to viscous constant. On the other hand, by vertical tapping, no significant change of all values of the dynamic parameter was recognized.3)When the distance between the roots was altered, an increase in distance between the roots lowered the dynamic parameter. The comparison between parallel and perpendicular percussion showed a large difference.4)When the location of the furcation area was altered, higher locations produced a lower dynamic parameter. There was no identifiable change regardless the ratio of elastic constant to viscous constant. There was also a significant difference between the result for paralleland perpendicular angle percussion.5)As compared two commercial instrument, "perio-test" and "tooth mobilitychecker" which were able to evaluate the mobility in quantitative manner, it was shown that newly developed device, damped oscillation system, was able to grasp the periodontium characteristics by introducing dynamic parameters. Less